1. Field of the Invention
The subject disclosure is directed to surgical implants, and more particularly, to fasteners for use with orthopedic bone plates for internally fixating and dynamically stabilizing fractured bones.
2. Description of Related Art
Bone fractures often require stabilization by internal fixation. Bone plates are among the most common orthopedic implants used to stabilize and internally fixate bone fractures. A typical bone plate is a rigid metal plate with guide holes through which bone screws can be passed. Bone screws are usually threaded into the bone above and below the fracture to secure the bone plate, thereby rigidly stabilizing and fixating the fracture.
There has been increasing emphasis on bone plates that are capable of providing compression of the fracture as well as stabilization. Most conventional compression plates however, are made of metal with a modulus of elasticity that is higher than that of bone and therefore, these compression plates have a limited ability to apply controlled amounts of compressive force to a fracture. Moreover, the use of such bone plates produces a mechanical system in which the majority of the stress is borne by the plate rather than the bone. This can impair the healing process in a fractured bone. Furthermore, it is now known that a controlled compressive load should be maintained across a fracture to promote rapid healing. Conventional, static bone plates do not provide or maintain such conditions.
An example of a dynamic vertebral column plate is disclosed in U.S. Patent Application Publication No. 2010/0234895 to Hess published on Sep. 16, 2010, the disclosure of which is herein incorporated by reference in its entirety for purposes of enablement.
Current practices using bone plates and screws to stabilize bone fractures include allowing the fastener to associate freely from the plate; using a tertiary cover to entrap the fastener; or providing a mechanism which prevents ejection, but allows for rotation. Free association of the plate and fastener provides no attachment method, and is inadequate where fastener ejection is not acceptable. A tertiary cap adds complexity to a construct, requiring additional assembly steps, each which have an additional mode of failure. The “ejection-only” designs allow a fastener to spin in the plating system, which can disassociate the plate from the anatomy it is fastened to, by backing the plate and fastener out as an assembly.